1. Field of the Invention
The present invention relates to an automatic focusing device and a focusing method, and in particular to an automatic focusing device and a focusing method, using an image pick-up element so as to carry out focusing.
2. Description of the Related Art
A voltage level of a high frequency component (high contrast part) contained in an image signal obtained by an image pick-up element corresponds to a focusing condition. In view of this phenomenon, there has been known an automatic focusing device for driving a focus lens to a position where the voltage level of a high frequency component is maximum so as to carry out focusing. Such an automatic focusing device is the so-called “hill-climbing servo system” or “contrast system”.
It is noted that in a conventional hill climbing servo system, an image signal is scanned in a horizontal direction for focusing so as to extract a high frequency component. Accordingly, it is difficult to precisely carry out focusing for an object to be picked up having no high frequency components in a horizontal direction, such as a horizontal stripe, even though the object to be picked up has a high contrast.
Thus, there have been proposed various measures for extracting high frequency components not only in a horizontal direction but also in a vertical direction so as to precisely carry out focusing even for an object to be picked up having no high frequency components in the horizontal direction.
For example, Japanese Patent Laid-Open No. H06-350902 discloses such a configuration that a pixel at a predetermined position is read out per one line in order to read out luminance signals stored in a memory in an obliquely 45 deg. direction.
Further, Japanese Patent Laid-Open No. 2002-303780 discloses such a configuration that an image at one frame is converted into luminance signals which are scanned in a focus detecting zone formed in a circular shape on a screen in a chordwise direction passing through the center of the circle in order to calculate a contrast value.
Further, Japanese Patent No. 2843981 discloses such a configuration that a high range frequency component is extracted from a low range frequency component, in a horizontal direction, of an image signal.